Process for preparing improved synthetic ester based grease compositions



United StatesPatent PROCESS FOR PREPARING IMPROVEDYSYN- ESTER BASED GREASE COMPO- Arnold J. Morway, Clark, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application June 23, 1954 Serial No. 438,853

6 Claims. (01. 252-32 This invention relates to improved synthetic oil based lubricating grease compositions and to processes for their preparation. Particularly, the invention relates to new grease compositions suitable for service over extremely broad temperature ranges which comprise synthetic lubricating oils thickened to a grease consistency with a complex salt-soap thickening agent. More particularly, the invention relates to a process for the formation of high temperature lubricating grease compositions which comprise preparing a synthetic lubricating grease by thickening a synthetic oil with a complex of a lower molecular weight salt and a high molecular weight soap, allowing the lubricating grease so formed to attain its maximum degree of hardness, blending with said hardened grease a minor amount of a synthetic lubricating oil and subjecting the diluted grease to the actions of high rates of shear at temperatures below about 200 F. to obtain the desired product.

It has been found in the past that lubricating grease compositions which are prepared by thickening a lubricating oil to a grease consistency with a complex of a low molecular weight acid salt and a high molecular weight fatty acid soap are extremely desirable for their extreme pressure resisting characteristics, high temperature resistance and long lubricating lives. It has more recently been found, however, that some of these complex lubricating grease compositions harden excessively on storage and that others that do not harden on storage have lubricating lives that make them less desirable for some applications. Generally speaking, when the mol ratio of the low molecular weight acid to the high molecular weight acid is below about 10:1, the grease compositions have excellent lubricating lives, but tend to harden excessively on storage. When the mol ratio of the low molecular weight acid salt to the high molecular weight acid soap is in excess of about 10:1, the grease compositions have a lesser tendency to harden on storage, but their lubrication lives are correspondingly decreased.

It has now been found and forms the object of this invention that complex lubricating grease compositions having long lubricating lives and yet little or no tendency to harden on storage may be obtained by a novel process. This novel process comprises the steps of thickening a synthetic lubricating oil to a grease consistency with a complex of a low molecular weight acid salt and a high molecular weight acid soap, wherein the mol ratio of said acid salt to said acid soap is below about 10:1, allowing the lubricating grease composition so'prepared to attain its maximum degree of hardness, diluting said hardened grease with an additional quantity of synthetic lubricating oil and subjecting said diluted grease composition to the action of high rates of shear under conditions of stream- EXAMPLE I Formulation (Mol ratio acetic acid to high mol weight acid=4:1):

ice

Ingredients-- Percent weight Hydroxystearic acid 9.81 Glacial acetic acid 8.45 Hydrated lime 5.62 Di-Z-ethylhexyl sebacate 75.12 Phenyl alpha naphthylamine 1.00

Preparation:

All ingredients except acetic acid and phenyl alpha naphthylamine were charged to a grease kettle and warmed to P. Then the acetic acid was added and the mass heated to 500 F. The mass was then cooled while working to 250 F. and phenyl alpha naphthylamine was charged. The grease was further cooled to- E.P. value=the Hertz line diameter is calculated from the formula determining the diameter of the contact area between two spherical surfaces. This diameter is the static indentation caused by deformation of the balls under load at the start of the test. This dimension is calculated as facgor (DH) where LDH is used to determine the corrected Corrected load=% L=Load (kg.)

DH=Hertz diameter XzAverage E.P. value=Number (15 minimum) of progressive runs.

EXAMPLE II A. A base grease having the following formulation was prepared 25.20% Glacial acetic acid 2.00% Hydrogenated castor oil 2.00% Hydrofoil acids 51 17.40% Hydrated lime 1.00% Phenyl alpha naphthylamine 52.40% Diisooctyl azelate Preparation:

This grease was prepared similar to that described in Example I.

B. A simple soap grease was prepared:

12.0% Hydroxystearic acid 1.6% Hydrated lime 1.0% Phenyl alpha naphthylamine 85.4% Diisooctyl azelate Preparation:

All the ingredients of B were charged to the Dopp steam kettle and mixed and reacted at 3l0-320 F. for 3 hours. 8.5% of the above described base grease A was then added and the mixture heated until thickening occurred (approximately 3 hours). The grease. was then rapidly cooled by passing water through the kettle jacket and they 'cold grease Gaulin homogenized. .The finished grease had the following formulation:

Patented June 30, 1959' 3 Formulation:

Ingredients-- Percent weight 12-Hydroxystearic acid 10.980 Hydrogenated castor oil 0.170

' Hydrofol acids 51 0.170 Glacial acetic acid 2.142 Hydrated lime 2.939 Phenyl alpha naphthylamine 1.000 Diisooctyl azelate 82.599

Properties:

Appearance Excellent Dropping point, F. 400

Penetrations, 77 F. mm./l Original 4 Days Later Unworkei. 255 162 Worked 60 strokes 304 204 Worked 100,000 strokes 370 368 Lubrication Life, Hours, 250 F.10,000 r.p.m

1,014: hours. bearing failure.

Test discontinued without a lubricant or It will be seen that the grease compositions of Examples I and II have excellent lubrication life but harden excessively on storage.

EXAMPLE HI Formulation (Mol ratio acetic acid to high molecular weight acid=20:1)

Ingredients Percent weight Glacial acetic acid 21.6 Hydrogenated castor oil 5.4 Hydrated lime u 15.0 Ortholeum 300 1.0 Diisooctyl azelate 56.0

Preparation: Similar to the grease described in Example I.

Properties: Meets all requirements of MIL-G-3278 specification.

Penetrations, 77 F. mm./ Original 1 Month Storage Unworked 275 271 Worked 60 strokes 293 290 El. value (4 ball test) 55 Lubrication Life, Hours, 250 F.-l0,000 r.p.m 410 1 See Example I above.

EXAMPLE IV EXAMPLE V Formulation (Mol ratio acetic acid to high molecular weight acid=10:1):

16.00% Glacial acetic acid 8.00% Hydrogenated castor oil 12.00% Hydrated lime 1.00% Phenyl alpha naphthylamine 63.00% Diisooctyl azelate Preparation: Similar to grease of Example I. Properties:

Appearance Excellent Storage Penetrations, 77 F. mm./l0

Origi- 3 days 60 days 76 days nal Unworked 139 195 103 Worked 60 strokes 297 225 201 205 Worked 100,000 strokes 310 Lubrication Life, Hours, 250 F.

10,000 r.p.m

1 No failure after 1,200 hrs.

After one month's storage or sooner the base grease penetration or consistency has stabilized showing no further hardening. This base grease is then cut back to desired consistency with additional diisooctyl azelate by mixing and Gaulin homogenization in the cold. Any increase in temperature over 200 F. during any manufacturing process will again result in the product becoming storage unstable.

OUT BACKS Formulations:

30 wt. 20 wt. percent percent Glacial acetic acid 11.2 12. 8 Hydrogenated castor oil- 5. 6 6. 4 Hydrated lime 8. 4 9. 6 Phenyl alpha naplithy1amine 0. 7 0. 8 Diisooctyl azelate 74.1 70. 4

Properties: Appearance Excellent 30 wt. 20 Wt. percent percent Penetrations, 77 F. mm./10:

Unworked 285 250 Worked 00 strokes 300 280 Worked 100,000 strokes 400 355 6 days storage- Unworked 265 248 Worked 60 strokes 293 275 16 days storage Unworked 275 251 Worked 00 strokes. 295 278 Dropping Point, F 500+ 500+ Lubrication Life, Hours, 250 F.l0,000 r.p.m 480 1, 108

No'rE.Test discontinued without failure. A

The synthetic lubricating oil used as a base for the lubricating greases of this invention are preferably the C to C branched chain alcohol diesters of dibasic acids. For instance, the dibasic acids having a formula Hooc cH, ,,cooH

wherein x is between about 2 and about 8, may be completely esterified with such alcohols as isooctyl, 2-ethylhexyl and other branched chain alcohols having from 6 to 16 carbon atoms. Especially preferred and contemplated in the preferred embodiment herein are the C to C branched chain alcohol diester of adipic, suberic, azelaic and sebacic acids, It is to be understood, however, that other synthetic lubricating oils may be used to prepare the inventive greases. Such materials as formals, complex formals, ethers, ether esters, glycol ethers, glycol esters, silicone fluids, carbonates, and the like may also be used for preparing the greases of the invention.

The complex salt-soap thickening agent used to prepare the greases of this invention may be present in a total amount of between about 5.0% to about 30%, the percentage being by weight, based on the weight of the total composition, depending upon the consistency desired in the final product. The low molecular weight acid used in the formation of the complex is preferably acetic acid. However, other saturated or unsaturated aliphatic car boxylic acids having about 1 to about 6 carbon atoms may be used. A partial list of such operable acids woul include Formic Acetic Propionic Butyric Furoic Acrylic Adipic and the like, including their hydroxy derivatives such as lactic acid, etc.

The high molecular weight acids used to prepare the complexes of the invention may be any of the commonly known grease making acids having from about 12 to about 30 carbon atoms, preferably from about 18 to 22 carbon atoms per molecule. These operable acids include stearic acid, hydroxy stearic acid, oleic acid, polyhydroxy stearic acid, arachidic acid, hydrogenated fish oil acids, tallow acids, etc. The metal used to form the low molecular weight acid salt and the high molecular weight acid soap are preferably the same metal, although different metals may be used. Whereas calcium is the preferred metal, other alkaline earth metals such as barium, magnesium and strontium may be used, although less desirable, the alkali metals such as sodium, potassium and lithium may be used under certain conditions. The preparation of the complex lubricating grease is set out in detail in Example I above and does not form an integral part of the instant invention. The gist of this invention lies in the discovery that once the complex grease composition attains its maximum hardness, very satisfactory grease compositions may be prepared by simply diluting the hardened grease with an additional amount of a synthetic lubricating oil, preferably, tho not necessarily, the same as used to form the lubricating grease and then homogenizing at high rates of shear under streamlined conditions. The amount of the additional synthetic lubricating oil which is added to the hardened grease composition will vary, depending upon the consistency desired in the final product, it being understood that increased dilution results in a less consistent material. Ordinarily, however, additional synthetic lubricating oil will be added in amounts such that the final complex content of the lubricating grease is within the range of from 5 'wt. percent to 30 wt. percent, with a preferred range being between about and about 25 wt. percent.

After the dilution step, the diluted grease is subjected to the action of high rates of shear, that is, in the order of from about 250,000 reciprocal seconds to about 750,000 reciprocal seconds under conditions of streamlined flow. Such equipment as a roller mill, a Gaulin homogenizer, a pressure viscosimeter and the like may be used to obtain this shearing action.

The complex greases prepared in accordance with the concept of this invention are perfectly compatible with the commonly used grease additive materials, for example, antioxidants such as phenyl alpha naphthylamine and the like may be incorporated into the grease formulation.

Other adidtives, such as tackiness agents, cooling bodies, extreme pressure resisting agents and the like may also be added to the grease compositions.

To summarize briefly, the instant invention relates to an improved process for the preparation of complex synthetic lubricating grease compositions. This process comprises the steps of thickening a synthetic lubricating oil, preferably a C to C diester of a dibasic acid, with from 5.0 wt. percent to about 30 wt. percent of a complex of a low molecular weight acid salt and a high molecular weight acid soap, the mol ratio of said salt to said soap being below about 10:1, allowing said lubricating grease composition to attain its maximum degree of hardness by remaining quiescent, diluting said hardened lubricating grease with a synthetic lubricating oil in an amount such that the thickening agent content remains between about 5.0 and 30.0 wt. percent and subjecting the diluted lubricating grease composition to the action of high rates of shear under conditions of streamlined flo'w.

What is claimed is:

1. A process for the preparation of new and useful lubricating grease compositions having extreme pressure resisting properties and having utility over broad temperature ranges which comprises the steps of thickening a synthetic diester lubricating oil as the sole base oil with a complex salt-soap thickening agent, the mol ratio of said salt to said soap being within the range of from 1:1 to 10:1, allowing said lubricating grease to remain quiescent until it has attained its maximum degree of hardness, blending with said hardened grease a minor but diluting quantity of additional synthetic oil sulficient to result in a mixture containing from about 5 to 30% by Weight of said thickening agent and subjecting the diluted grease to the action of high rates of shear in the order of from about 250,000 to 750,000 reciprocal seconds under streamlined conditions at temperatures below about 200 F. to obtain a finished grease composition.

2. A process according to claim 1 wherein said synthetic lubricating oil is the C to C alcohol diester of a. dibasic acid.

3. A process according to claim 1 wherein said synthetic oil is di-2-ethylhexyl sebacate.

4. A process according to claim 1 wherein said synthetic oil is di-isooctyl azelate.

5. A process according to claim 1 wherein said salt is the calcium salt of acetic acid.

6. A process acording to claim 1 wherein said soap is the calcium soap of a high molecular weight fatty acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,263 Carmichael et a1 Apr. 16,1940 2,607,735 Sproule et al Aug. 19, 1952 2,704,363 Armstrong Mar. 15, 1955 2,750,341 Morway et a1 June 12, 1956 2,758,973 Morway et a1. Aug. 14, 1956 

1. A PROCESS FOR THE PREPARATION OF NEW AND USEFUL LUBRICATING GREASE COMPOSITIONS HAVING EXTREME PRESSURE RESISTING PROPERTIES AND HAVING UTILITY OVER BROAD TEMPERATURE RANGES WHICH COMPRISES THE STEPS OF THICKENING A SYNTHETIC DIESTER LUBRICATING OIL AS THE SOLE BASE OIL WITH A COMPLEX SALT-SOAP THICKENING AGENT, THE MOLE RATIO OF SAID SALT TO SAID SOAP BEING WITHIN THE RANGE OF FROM 1:1 TO 10:1, ALLOWING SAID LUBRICATING GREASE TO REMAIN QUIESCENT UNTIL IT HAS ATTAINED ITS MAXIMUM DEGREE OF HARDNESS, BLENDING WITH SAID HARDENED GREASE A MINOR BUT DILUTING QUANTITY OF ADDITIONAL SYNTHETIC OIL SUFFICIENT TO RESULT IN A MIXTURE CONTAINING FROM ABOUT 5 TO 30% BY WEIGHT OF SAID THICKENING AGENT AND SUBJECTING THE DILUTED GREASE TO THE ACTION OF HIGH RATES OF SHEAR ON THE ORDER OF FROM ABOUT 250,000 TO 750,000 RECIPROCAL SECONDS UNDER STREAMLINED CONDITIONS AT TEMPERATURE BELOW ABOUT 200* F. TO OBTAIN A FINISHED GREASE COMPOSITION. 